[PATCH v2] examples/dma: support DMA dequeue when no packet received

[Bruce Richardson]

On Mon, Jul 25, 2022 at 08:22:00PM +0800, Chengwen Feng wrote:
> Currently the example using DMA in asynchronous mode, which are:
> 	nb_rx = rte_eth_rx_burst();
> 	if (nb_rx == 0)
> 		continue;
> 	...
> 	dma_enqueue(); // enqueue the received packets copy request
> 	nb_cpl = dma_dequeue(); // get copy completed packets
> 	...
> 
> There are no waiting inside dma_dequeue(), and this is why it's called
> asynchronus. If there are no packet received, it won't call
> dma_dequeue(), but some packets may still in the DMA queue which
> enqueued in last cycle. As a result, when the traffic is stopped, the
> sent packets and received packets are unbalanced from the perspective
> of the traffic generator.
> 
> The patch supports DMA dequeue when no packet received, it helps to
> judge the test result by comparing the sent packets with the received
> packets on traffic generator sides.
> 
> Signed-off-by: Chengwen Feng <fengchengwen at huawei.com>

Acked-by: Bruce Richardson <bruce.richardson at intel.com>